Torque, Base of Support, Moments of Force

torque

turning effect produced by a force, known as "moment of force" or "moment", causes change in angular motion

muscles

create torque about joints

three types of force

centric force, eccentric force, and force couple

centric force

force line of action directed through center of gravity, causes change in translation only, linear only

eccentric force

force line of action not directed through center of gravity, causes changes in translation and rotation, linear and angular

force couple

2 eccentric noncolinear forces, equal and opposite in direction, causes changes in rotation only, angular only

moment arm

perpendicular distance between the line of action of a force and specified axis of rotation, shortest line between line of action of a force and an axis, represented by "r"

longer moment arm

increases turning effect of a force

shorter moment arm

decreases turning effect of a force

torque equation

f x r
f= force (N)
r=moment arm (m)
units- Nm (Joule)

description of torque

specified axis of rotation
magnitude of the force
sense (direction) of the torque

given size torque being created

large force on short movement arm, small force on long moment arm

tools

allow humans to increase torque, humans produce variable amounts of force, these typically increase moment arm to increase applied torque

muscular torque

muscle produces a pulling force, every muscle crosses a joint, muscle has a moment arm about the joint axis

internal torque

muscle producing torque on a joint

muscle moment arm

length varies as a joint rotates

external torque

load outside of the body producing torque on a joint

isometric load

internal torque is equal to external torque

concentric load

internal torque is greater than external torque

eccentric load

external torque is greater than internal torque

resistance torques

created at joints by exercise weights, opposed by muscle torque, varies as machine moves through ROM

weight torque

in strength training: increases as moment arm gets longer and decreases as moment arm gets shorter

resistance moment arm

perpendicular distance from line of action of the cable to the axis of the machine arm

center of gravity

point in a body or system where the entire mass is evenly distributed, imaginary point in space, not fixed: changes when parts of an object change position, point of balance

center of gravity in human body

location depends on position of each limb, location can be outside of the body

female center of gravity

55% of height

male center of gravity

57% of height

cg shifts left

lifting left arm away from side

cg shifts forward

lifting left arm in front of body

cg shifts upward

raising both arms away from side

stability

capacity of a body to return to equilibrium when displaced, not easily moved or thrown off balance

factors of stability

height of center of gravity, size of base of support, weight of object

more stable

lower, wider, heavier

less stable

smaller base of support